Introduction : Hepatitis delta virus (HDV) infection is rare in Japan. The chronic infection rate of HDV is less than 1.0% among hepatitis B surface antigen (HBsAg)-positive Japaneses. However, a high prevalence rate of anti-HDV has been observed among inhabitants of Miyako Island of Okinawa Prefecture in Japan. The present investigation attempted to reveal the precise prevalence of HDV infection among inhabitans of this island and molecular characteristics of the HDV genome isolated.Patients and Methods : An periodic health check was performed for 4,728 inhabitans of Miyako Island in 1996. HBsAg-positive subjects were 375 (7.9%) among 4,728 by EIA method. Anti-HDV was positive in 32 (8.5%) among these 365 subjects by RIA method. Sera from these 32 subjects were analyzed for the further viral investigation. HDV RNA was extracted from each 100 micro liter serum and served for nested RT-PCR using primer pairs (first nt 695-718 and nt 873-896 ; second nt 726-745 and nt 846-865). The neste
… Mored PCR products of 6 subjects were sequenced, followed by nucleotide homology investigation.Results : The nested PCR successfully amplified HDV cDNA in ten (31.3%) out of the 15 subjects. The nucleotide sequence of these seven HDV cDNA were classified into two major groups. One (A) group consisted of 4 genomes and the other (B) group consisted of 3 genomes. While nucleotide homology was 94.6-98.0% among Group A and 96.1%-98.1% among B, that between Group A and Group B was 84-88%. Nucleotide homology of Group A and B with the 2 previously reported Japanese isolates was 92.1-98% and 82.4-86%, respectively, The homology with the previously reported isolates outside Japan was 41.5-96.2% for Group A and 41.0-86.2% for Group B.Pylogenic analysis showed Miyako isolates were classified into genotype I.Conclusion : HDV isolates of Miyako island are classified into genotype I and their genotype differs from that of Japan outside Miyako island. Genetic analysis suggests that HDV in Miyako island may be related phylognically with Lebanon, Nauru, and South Europe. It is unclear why HDV infection is prevalent in the isolated island ; however, the further genome investigation will provide us a clue of the route of high infection and interesting informations of molecular evolution of HDV genomes. Less